I think there would be nice hiding places and all the different fairytale parts would make the gameplay interesting.
But as you already said the map might be a "bit" too big for a Hide n Seek map I´m not sure if the seekers would even have a chance to find all of the hiders. Propably not.

No idea. Maybe just condense most of the open space so there's less room in general? There's a TON of open space on the map, but that's because SG needs big maps. I just love the aesthetics of the map.